Be sure that the cam is not locked in the down position. Open it. Grease it where the plunger meets the cam. Let the rudder drop against the lower casting and lower the upper arm to lock. If none of this helps... Possibly the upper casting "cam adjustment" plate or the rudder mounting holes are wrong or the cams are damaged / worn where they would catch the upper casting. If that part is bent open or is too flexible, the cam should be replaced.

Inside the casting attached to the rudder blade there is a plastic screw; you have to access it from the bottom.
Having an '82 H14 turbo myself, I would guess that the plastic is hard as stone, won't move a hair if you try to use a screwdriver and the slot will just wear out.

Works great, just did it a month ago. In order to remove the old plastic bolt, I first drilled it out being carefull not to damage the threads, and then used a small propane torch to burn the remains out of the threads.